Recently, with an increase in social request for energy saving, a requirement for reducing fuel consumption of automobiles has become more severe. For coping with such a requirement, further reduction of rolling resistance has been demanded with regard to tire performance. As a method for lowering the tire rolling resistance, besides a method for optimizing a tire structure, a method of using less heat-generating one as a rubber elastic body constituting the tread has been most commonly investigated.
For obtaining such a less heat-generating rubber elastic body, a rubber composition using silica or carbon black as a filler has hitherto been investigated. As such a rubber elastic body, for example, there has been proposed one containing a modified conjugated diene polymer, in which a polymerization active end of a conjugated diene polymer obtained by anionic polymerization with using an organolithium compound is modified with a compound containing a functional group that interacts with the filler, as a rubber component (see Patent Document 1).
On the other hand, as a rubber composition providing a rubber elastic body having good balance between low rolling resistance and wet skid resistance, there has been proposed one comprising carbon black and a modified block copolymer comprising a polymer block having a high glass transition temperature and a polymer block having a low glass transition temperature, in which an end of the polymer block having a low glass transition temperature is modified with a compound containing a functional group (see Patent Document 2).
However, in the above rubber composition, there is a problem that the filler to be used is limited to carbon black and a rubber elastic body having both of excellent low rolling resistance and wet skid resistance is not obtained although a balance between low rolling resistance and wet skid resistance is improved.
Moreover, although there has been proposed a rubber composition providing a rubber elastic body having an excellent balance between low rolling resistance and wet skid resistance in the case where silica is used as a filler, further improvement has been required.